Is it safe to Chrome coat 4340? 1

[jack70]

Our shop reworked 4340 tube stock (AMS 6414) and created an area of undersize outer diameter.
It was proposed to chrome coat the affected surface and machine again to proper finish OD.

Would there be any deleterious effect? Hydrogen embrittlement, etc?
Is there a better process to build up or fill in the surface?

The stock is subsequently cad plated, heat treated to Rc 32-36, shot peened, epoxy primed, and painted black.

The final part is a critical aircraft part.

 

[unclesyd]

Off hand I would say No. I believe in this situation a new part is required.

Aside from this being a critical part there are too many subsequent operations on the affected part that chrome plating would interfere with or prevent.

 

[jack70]

Correction, the area to be chrome coated is not cad plated, shot peened, or painted.

 

[dbooker630]

I remember doing a lot of chrome plating/finish grinding on ball bearing OD's back in the late 70's and early 80's.

Recently, I have had 4340H shafts chrome plated, also on undersize diameters, but after induction hardening and furnace tempering. An additional temper cycle was performed after the plating.

I also recommend getting customer approval on an engineering deviation since it appears you are dealing with a safety related component.

 

[metengr]

The final part is a critical aircraft part.

IMO, the statement says it all, I would not recommend it.

 

[arunmrao]

I second metengr. I missed reading the last line of the OP.

Chocolates,men,coffee: are somethings liked better rich!!
(noticed in a coffee shop)

 

[Helicopterjunky]

Chrome build-up has been done for years on aircraft components. However, the order of operations you list is not typical. Normal sequence is that part is already heat treated to required core strength level. Area to be built-up is ground undersized (ODs) or oversized (IDs). Area to be chromed is shotpeened and then chrome plated oversize. A bake immediately after chrome plating is performed to drive off hydrogen. This bake is a must, even for your reduced strength level. The Chrome plated area is ground again to proper final size. Many critical aircraft parts are re-sized this way. Keep in mind when reworking an already fielded part, which has a defined fatigue life, most of it could be used up by the time you see it for re-work. If these are new parts as you seem to indicate it should not be a problem. Remeber have heat treat completed before re-size.

 

[plasgears]

Consider nickel plating as a more machinable rework surface.

 

[israelkk]

Back on 1973 I have encountered the same process as Helicopterjunky posted to rework 4340 shaft for aerospace application. As far as I recall it was the main shaft/axis of an aircraft landing gear wheel.